A method and a control unit for controlling an internal combustion engine is known from DE 100 56 862 C1, for example.
This prior art is concerned with a special “strategy” for injecting a preliminary fuel injection into each cylinder when starting the engine (internal combustion engine), even before a complete knowledge (“synchronization”) of the crankshaft angle and of the camshaft angle is available.
Preliminary injections serve to provide each cylinder with an ignitable mixture for the first combustion during the starting phase. In this case, a specific preliminary injection strategy is required in order to minimize emissions of unburned fuel and hence increased pollutant emissions during engine starting.
Admittedly, it would be possible to avoid excessive pollutant emissions by outputting the preliminary injections only when the precise angular positions of the crankshaft and the camshaft are known. Owing to the customary configuration of crankshaft and camshaft sensors, however, this requires a certain time or crankshaft and camshaft rotation, and therefore engine starting would be considerably delayed.
The preliminary injection strategy provided by DE 100 56 862 C1 is based on the knowledge that an internal combustion engine almost always comes to a halt at one of a number of particular discrete angular positions of the crankshaft and the camshaft in the decoupled state after being switched off, there being several such positions owing to the design and the number of discrete angular positions over two crankshaft revolutions)(720°) corresponding to the number of cylinders. In the case of 4 cylinders, for example, there are therefore 4 preferential stoppage angles of the crankshaft. Even when this knowledge is allowed for when evaluating the crankshaft signal and camshaft signal during the starting phase, there remains a degree of uncertainty with this known strategy. Admittedly, in the illustrative embodiment described, it is, for example, ensured that preliminary injections are output only for cylinders on which the inlet valve is closed or predominantly closed at this point in time, and therefore combustion of these preliminary injections is reliably ensured. However, it is disadvantageous that an earlier point in time that is in fact already suitable for a preliminary injection may be “missed”.